(Left) PARSEC stellar isochrones for 9, 9.5, and 10 Gyr with a fixed metallicity of −0.5. The source is most likely an old subgiant. (Middle) Source angular radius based on the spectra models as a function of the source distance and age (color-coded). The points are derived from the template matching MCMC chains and the stellar isochrones. (Right) Source distance based on the Gaia source measurements from the model (G _s ∼ 16 mag) and the extinction estimated from the template matching modeling. Black dashed lines indicates the 1σ confidence region from the parallax measurement of Gaia.